The objective of the proposed research is to develop and apply the techniques of gas chromatography-mass spectrometry and high-pressure-liquid-chromatography to analyze DNA-modification and its biological role. DNA from various organisms will be examined for the nature/level of methylated (or otherwise modified) bases (e.g., 5-methylcytosine, N6-methyladenine, 1-3 or 7 methylguanine). Among the systems to be investigated are: (1) the mealybug (to study the connection between DNA-modification and facultative heterochromatization); (2) the sea urchin (to study the connection between DNA-modification and differentiation), (3) rat mammary tumors (to study the connection between DNA-modification tumor induction, and the role of hormones in these processes). In addition, we will examine DNAs from unicellular eukaryotes, as well as from bacterial and animal viruses.